C. elegans (nematode worm)
Nematode worms are now used extensively in biological research, the most commonly used being the tiny roundworm Caenorhabditis elegans. It is easy to breed, has a well studied genome, and many generations are born in a time-frame of days. It is susceptible to environmental changes and mutations, and the effects of these can be seen on later generations within a short experimental timeframe. C. elegans has a small nervous system, with only 302 neurons making known synaptic connections. This tiny nervous system carries out many of the same functions as the nervous systems of higher organisms, and is often studied as a model to help understand the basic mechanisms behind complex behaviours.
The discovery of novel antibiotics
C. elegans are used to identify chemicals with antibiotic properties through screening a vast array of possible candidates. The process involves infecting worms by laying them in a dish of pathogenic bacteria for 15 hours before a particle sorter is used to drop a precise number of the infected worms into small wells. Each of the 384 wells on a plate is loaded with a different, potentially-antibiotic chemical. The particle sorter distributes 15 worms into each well, and these are left for five days before they are examined to determine whether the worms survived their infection, which would indicate they were in contact with an antibiotic.
A new process involves exposing the worms to an orange dye at the end of five days. This dye is able to enter dead cells but not living ones, enabling researchers to identify the living worms more easily. The process of checking the wells can be easily automated as differences in contrast can be measured busing a camera and computer, in a process which allowed the team who developed it to identify 28 antibiotics (of 37,000 compounds tested). Importantly, some of these compounds work by different mechanisms to existing antibiotics, allowing them to bypass existing bacterial resistance.
How sensory input leads to behaviour
A team have investigated how C. elegans ‘smells’ food, triggering receptors, which in turn activate particular nerve pathways and lead to certain types of movement, enabling the worm to reach its food source. Despite the clear differences, this particular piece of ‘circuitry’ shares many features with the way that the retina senses light in mammals, and how this information is used by the brain to initiate other tasks.
Lamarck’s blacksmiths and the worm’s genes
In the late 18th and 19th centuries it was observed that the son’s of blacksmiths had stronger arms than the sons of weaver. Now, if you’d asked a biologistto explain that observation today you’d probably get a series of questions such as who observed this? Where did they grow up? What did the mother look like? What is the sample size? Or even, can we swap the children at birth?...
The muscles of the blacksmiths and their sons are responding to their environment, and although this represents quite a trivial example of such an interaction the phenomenon is widespread and there are many fascinating examples to be found in nature. For example, C Elegans has a quite striking interaction with its environment, such that under conditions unfavourable for reproduction, instead of developing as an adult it can go into a form of stasis, developing into an arrested stage that is both environmentally resistant and long lived. Once environmental conditions improve the arrested worm resumes development, growing into a perfectly normal adult.
Extract from the full article in University of Bristol, Research News, May 2005.
- Sreekanth H. Chalasani et al. (2007) Nature 450, 63